A pressure sensor module contains, for example, piezoresistive sensor cells, which are used for a broad range of applications, for example a pressure measurement in an intake manifold of a motor vehicle. In this connection, a pressure sensor chip is soldered to a socket, which has glass feedthroughs for external electrical connections. Then electrical connections of the pressure sensor chip are electrically contacted with the external electrical connections by means of bonding wires.
The pressure of a medium acts, for example, on a back side of the pressure sensor chip by means of a metal tube, which is soldered to the socket. For absolute pressure measurements, a metal cap is welded to the socket under vacuum. For relative pressure measurements, the cap has an opening. The pressure sensor chip is protected, for example by means of a gel, against external influences. A sensor cell of this kind cannot be used with intensely corrosive mediums since the corrosive medium corrodes the sensor chip or the gel.
JP 2000 046 666 A1 has disclosed a pressure sensor module in which the sensor membrane is protected by a gel in the pressure fitting. However, this gel is also corroded by the corrosive medium and since as a gel, it does not have great chemical resistance or mechanical strength, it changes in shape over time, which has an influence on the measuring results.
To this end, according to the prior art, the pressure is indirectly transmitted to the pressure sensor chip by means of a separating membrane and a pressure transmitting medium, e.g. silicon oil. The design of such a pressure sensor module, with this oil seal is known, for example, from the AMA seminar tape, 1989, pp. 285 to 295. In this design, the oil volume around the pressure sensor chip is relatively large. Due to the high thermal volume expansion coefficient of the silicon oil in comparison to the volume expansion coefficient of a housing material, the separating membrane is deflected in the event of a temperature change. Due to a non-negligible rigidity of the separating membrane, a pressure then builds up on the pressure sensor chip in the pressure sensor module, which is due solely to the temperature change and distorts the measurement signal.
In order to reduce the oil volume in the known pressure sensor module, the oil volume around the pressure sensor chip is reduced, e.g. by means of a filling body made of ceramic. In this instance, the filling body requires a separate assembly step. In the known pressure sensor module, due to the relatively high manufacturing tolerances, there is a large oil volume for the cavity around the pressure sensor chip in comparison to the cavity underneath the separating membrane.
As a result, for greater measurement precision, it is necessary to calibrate the pressure sensor chip when it is filled with oil. In this connection, the amount of time required to complete the temperature steps during calibration is longer since there is a higher heat capacity. In addition, in the known pressure sensor module, a defect of the pressure sensor chip can only be detected once it is completely assembled. As a result, the costs arising from rejections are higher since the finished component has to be discarded.
DE 195 07 143 A1 and U.S. Pat. No. 5,595,939 have disclosed a pressure sensor module according to the principal of the oil seal, with a simpler assembly process. In this pressure sensor module, the filling body for reducing the oil volume is replaced by a recess for the pressure sensor chip in the plastic plug connector housing. In this instance, a sealing of the separating membrane in relation to the plug connector is produced by means of an O-ring or a crimped seal. With this type of seal, there is the danger, for example in the event of a damaged O-ring or when particles adhere to the sealing surface, of oil escaping from the interior of the sensor. In the pressure sensor module, when the module is being filled with oil, the exertion of a high pressure on the separating membrane forces the residual air enclosed in the sensor out from the plastic material, which allows the air molecules to pass through. In this connection, there is the danger of the pressure sensor chip, which is designed for low pressure measurement ranges, being damaged by the high pressure for displacing the residual air in the housing.
For the pressure sensor chip, further steps are required to improve the electromagnetic compatibility, by means of capacitors, for example. The integration of these capacitors into the housing in the known sensor module is complicated and increases the manufacturing costs for the pressure sensor module.
JP 2000 009 568 A1 has disclosed a pressure sensor module in which an adapter is connected to a pressure sensor cell in order to determine the pressure of a fluid. The design is very complex and includes a large dead volume of the transmitting medium.
JP 11 316 166 A1, DE 44 15 984 A1, and U.S. Pat. No. 5,629,538 have disclosed pressure sensor chips, which have a protective film on the sensor membrane in order to protect it from a corrosive environment. This protective layer changes the reaction behavior and measurement behavior of the membrane in a negative fashion and also does not offer sufficient protection over a long time since this protective layer must be thin enough to allow the sensor membrane to continue to flex in a favorable fashion.
JP 81 36 380 A1 has disclosed a pressure sensor module, which is connected to an adapter in order to protect the pressure sensor chip from the corrosive medium. In this design, an O-ring must once again be used to produce a seal, which brings about the O-ring-related problems described above.